1. Field
The disclosed technology relates to sound speed measurement.
2. Description of the Related Technology
The enormous heat capacity of the upper ocean relative to the atmosphere gives it a major role in the regulation of Earth's climate. Monitoring the spatial and temporal variability of heat content of the upper 1000 meters or so of the world's oceans is therefore of great interest. As the temperature and speed of sound are related via well-known formulae, measuring the speed of sound at various points in time and space gives this information.
The speed of sound in water increases with increasing water temperature, increasing salinity, and increasing depth. Most of the change in sound speed in the surface ocean is due to changes in temperature. This is because the effect of salinity on sound speed is small and salinity changes in the open ocean are small. Near shore and in estuaries, where the salinity varies greatly, salinity can have a more significant effect on the speed of sound in water. As the depth increases, the pressure of the water has the largest effect on the speed of sound.
A relation between propagation speed (velocity) as a function of depth, is called the sound speed profile, or sound velocity profile, and it is a fundamental tool for predicting how sound will travel. Neglecting salinity, the sound speed can be obtained from sampling the ambient temperature at various depths. An inexpensive probe to do this is called an expendable bathythermograph (XBT). However, a need exists for other mechanisms, e.g. acoustics mechanisms, for remotely measuring the average speed of sound to a particular depth, or a sound speed profile, to provide the temperature of the water at various points.